Silicone compositions have long been used as release coatings, which render surfaces or materials comparatively nonadherent to other materials which would ordinarily adhere thereto. Silicone release compositions are widely used as coatings which release pressure-sensitive adhesives on labels, decorative laminates, transfer tapes, etc. Silicone release coatings on paper, polyethylene, Mylar.RTM., and other such substrates are also employed to provide non-stick surfaces for food handling and industrial packaging applications.
Silicone paper release coatings are effeciently applied from an aqueous bath containing the emulsified silicone coating composition and a catalyst emulsion. Once coated, the paper or other substrate is exposed to heat in order to cure the coating.
Silanol-containing paper release compositions are catalyzed by organo tin compounds, as disclosed in U.S. Pat. No. 3,499,870 (Hadlock et al.), and extensive work has been performed in achieving the optimal combination of properties in these catalysts. See, e.g., U.S. application Ser. No. 356,796 filed Mar. 10, 1982, now U.S. Pat. No. 4,426,490 and commonly assigned.
Catalysts prepared for use in water base systems must be emulsified with such conventional emulsifiers as polyvinyl alcohol. A drawback to these catalyst emulsions has been that they can separate with time on storage, or they can break with exposure to temperature extremes, i.e., below about -15.degree. C. or about 50.degree. C. Some tin compounds may also undergo hydrolysis during prolonged storage and revert to catalytically inactive form.
It has now been discovered that these drawbacks can be overcome by novel blends including an emulsifier and an organo tin catalyst which are self-emulsifiable (i.e., water dispersible) and so can be added to paper release coating baths without pre-emulsification. The blends form uniquely stable catalyst emulsions which remain active longer when stored in emulsion form than known catalyst emulsions.